Lithography techniques include processes in which, for example, a resist film formed from a resist material is formed on top of a substrate, the resist film is selectively exposed with irradiation such as light, an electron beam or the like through a mask in which a predetermined pattern has been formed, and then a developing treatment is conducted, thereby forming a resist pattern of the prescribed shape in the resist film. Resist materials in which the exposed portions change to become soluble in a developing solution are termed positive materials, whereas resist materials in which the exposed portions change to become insoluble in the developing solution are termed negative materials.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used; however, nowadays, KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use F2 excimer lasers, electron beams (EB), extreme ultraviolet radiation (EUV) and X-rays.
Resist materials are required to have lithography properties such as high sensitivity to the aforementioned light source and sufficient resolution to reproduce patterns with a very fine size. As resist materials which fulfill the aforementioned requirements, a chemically-amplified resist containing a base resin that displays changed solubility in an alkali developing solution under action of an acid, and an acid generator that generates an acid upon exposure are known.
For example, a chemically-amplified positive resist includes a resin in which the alkali solubility increases under action of an acid as a base resin and an acid generator, and when an acid is generated from the acid generator upon exposure in the formation of a resist pattern, the exposed portions are converted to a soluble state in an alkali developing solution.
Until recently, polyhydroxystyrene (PHS) or derivative resins (PHS-based resins) in which the hydroxyl groups within polyhydroxystyrene have been protected with acid dissociable, dissolution inhibiting groups, which exhibit a high degree of transparency relative to KrF excimer laser (248 nm), have been used as the base resin of chemically-amplified resists (For example, see Patent Document 1).
Examples of the acid dissociable, dissolution inhibiting groups include so-called acetal groups, such as chain-like ether groups typified by 1-ethoxyethyl groups, and cyclic ether groups typified by tetrahydropyranyl groups; tertiary alkyl groups typified by tert-butyl groups; and tertiary alkoxycarbonyl groups typified by tert-butoxycarbonyl groups.
On the other hand, as acid generators usable in a chemically-amplified resist, various types have been proposed including, for example, onium salt-based acid generators such as iodonium salts and sulfonium salts; oxime sulfonate-based acid generators; diazomethane-based acid generators; nitrobenzylsulfonate-based acid generators; iminosulfonate-based acid generators; and disulfone-based acid generators. Currently, as acid generators, those which include a triphenylsulfonium skeleton, dinaphthyl monophenylsulfonium skeleton or the like are used (for example, see Patent Document 2).